| AVS 66th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Monday Sessions |
| Session PS+AS+EM+SS+TF-MoA |
| Session: | Plasma-Surface Interactions |
| Presenter: | Adam Pranda, University of Maryland, College Park |
| Authors: | A. Pranda, University of Maryland, College Park K.-Y. Lin, University of Maryland, College Park G.S. Oehrlein, University of Maryland, College Park |
| Correspondent: | Click to Email |
The emergence of atomic layer etching (ALE) processes has enabled improved control of surface profiles. Whereas the implementation of ALE processes on hard mask materials has been well established, the effects of these processes on photoresist materials is not well known. With the advent of next generation extreme ultraviolet (EUV) photoresists, there is the potential to utilize ALE processes with photoresist materials for fabrication of sub-10 nm feature sizes.
The plasma processing of photoresist materials induces several key physical and chemical modifications which affect material properties such as the etching behavior and surface roughness. In this work, we utilize in-situ ellipsometry, atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy to interpret the relationships between the aforementioned material properties, the photoresist chemical composition, and plasma ALE parameters such as ion energy and precursor gas type. By comparing these relationships between baseline continuous plasma etching processes and ALE processes, which include the introduction of chemically reactive surface passivation, we elucidate the intrinsic photoresist behaviors under plasma exposure and how an ALE process specifically impacts these behaviors.
Under nonreactive plasma chemistries, a universal response among photoresist materials is the development of a surface dense amorphous carbon (DAC) layer due to energetic ion bombardment. We have found that the photoresist etch rate is inversely proportional to the DAC layer thickness.1 However, photoresists with UV sensitive pendant groups, such as 193 nm photoresists, develop a greater surface roughness due to the stresses in the surface generated by synergistic ion and UV photon interactions.
With depositing fluorocarbon (FC)-based ALE gas chemistries, the deposited FC layer reacts with the DAC layer and converts it into a mixed layer. This incorporation of FC into the DAC layer reduces the surface roughness without impacting the etch rate of the underlying photoresist as long as a sufficient DAC layer thickness remains.2 This behavior is potentially advantageous for maximizing the photoresist to SiO2 selectivity while maintaining an adequate surface roughness.
The authors acknowledge S.A. Gutierrez Razo, J.T. Fourkas, R.L. Bruce, S. Engelmann, and E.A. Joseph for collaborations on aspects of this work, and financial support by the National Science Foundation (NSF CMMI-1449309) and Semiconductor Research Corporation (2017-NM-2726).
1 A. Pranda et al., J. Vac. Sci. Technol. A 36, 021304 (2018).
2 A. Pranda et al., Plasma Process. Polym. e1900026 (2019).